The present invention relates to the field of mass storage devices. More particularly, this invention relates to an improved apparatus and method for securing a portion of a high density disc drive during a servo track writing operation.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc drive housing, a disc that is rotated, an actuator assembly that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
To read and write data to the disc drive, the actuator assembly includes one or more arms that support the transducer over the disc surface. The actuator assembly is selectively positioned by a voice coil motor which pivots the actuator assembly about a pivot shaft secured to the drive housing. The disc is coupled to a motorized spindle which is also secured to the housing. During operation, the spindle provides rotational power to the disc. By controlling the voice coil motor, the actuator arms (and thus the transducers) can be positioned over any radial location along the rotating disc surface.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equalize so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on portions of the storage disc referred to as tracks. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto the track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write to or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is often divided between several different tracks. While most storage discs utilize a multiplicity of concentric circular tracks, other discs have a continuous spiral forming a single track on one or both sides of the disc.
During manufacture, servo feedback information is encoded on the disk and subsequently used to accurately locate the transducer. The servo information is used to locate the actuator assembly/transducer head at the required position on the disc surface and hold it very accurately in position during a read or write operation. The servo information is written or encoded onto the disc with a machine commonly referred to as a servo track writer (hereinafter STW). At the time the servo information is written, the disc drive is typically at the xe2x80x9chead disk assemblyxe2x80x9d (hereinafter HDA) stage. The HDA includes most of the mechanical drive components but does not typically include all the drive electronics. During the track writing process, the STW precisely locates the transducer heads relative to the disc surface and writes the servo information thereon. Accurate location of the transducer heads is necessary to ensure that the track definition remains concentric. If the servo track information is written eccentrically, the position of the transducer head during subsequent operation will require relatively large, constant radial adjustments in order to maintain placement over the track center. When the tracks are sufficiently eccentric, a significant portion of the disk surface must be allotted for track misregistration. Accordingly, overall track density is degraded and disc drive capacity is reduced.
In order to ensure proper writing of servo information, STWs utilize an external, closed loop positioning system that precisely positions the transducer head during servo track writing. The positioning system comprises a contact member that engages the actuator assembly, a position indicator which indicates the position of the contact member, and a displacing mechanism which repositions the contact member based on feedback from the position indicator. To ensure accurate positioning, various position indicators are used (e.g., mechanical, capacitive, and optical transducers to name a few). The STW further includes the required circuitry for writing the servo information to the disc surface via the transducer heads.
As demand for higher capacity drives grows, manufacturers are constantly seeking to increase drive capacity by increasing track density. That is, by increasing the density or xe2x80x9ctracks per inchxe2x80x9d (TPI), a greater number of discreet tracks can be encoded on a given disc surface. However, higher track density requires more efficient use of the disc surface. Accordingly, track misregistration due to eccentricities in track formation must be minimized in order to maximize TPI (and thus disc capacity).
While it is advantageous to maintain substantial concentricity during the servo track writing process, many factors adversely impact the STW""s ability to write servo information concentrically. For instance, induced resonance in the STW itself can adversely affect the track writing operation. Further, vibrations in the spindle or actuator components (e.g., imperfect bearings) may also produce non-repeatable track writing errors. Still yet another problem with current STWs is oscillations in the HDA itself (i.e., independent deflection of the actuator and spindle relative to the STW). The present invention is directed to reducing these problems, especially the effects of component deflection, and the remainder of this discussion will focus on the same.
Most current STWs support the HDA by engaging a plurality of points on the external drive housing. When the HDA is so engaged, the spindle and actuator are restrained only by the internal structure of the HDA (i.e., the drive housing). Still other HDAs fasten the drive cover to the pivot shaft and a spindle shaft to provide additional support thereto. However, these STW/HDA configurations still produce drives with limited track densities not because of the STW""s positioning accuracy but rather because of the non-repeatable deflection and vibration of the HDA components.
Accordingly, what is needed is an apparatus and method for use with an STW that minimizes relative deflection between the components of the HDA during the track writing process. In particular, what is needed is a way to reduce HDA component deflection sufficiently to allow greater track densities to be formed on a given disk surface. The present invention addresses these needs.
In devising the method and apparatus of the present invention, the inventors realized that current STW systems were limited in the maximum track densities they could achieve. To address this problem, the inventors focused on a method and apparatus for securing the drive during the track writing process.
In one embodiment, a method of restraining a head disk assembly (HDA) within a servo track writing apparatus (STW) is provided. The HDA includes a housing and a spindle shaft coupled to the housing where the spindle shaft rotatably supports a spindle having at least one storage disc. The HDA further includes a pivot shaft coupled to the housing. The pivot shaft pivotally supports an actuator assembly for moving a transducer head relative to the disc. The method comprises the steps of placing the HDA into the STW where the STW has opposing clamp members with opposing contact points. The HDA is then clamped between the clamp members such that the contact points operatively engage each end of both the pivot shaft and spindle shaft. A compressive load is then applied to the HDA, wherein the opposing contact points load against the ends of the pivot shaft and the spindle shaft to restrain non-rotational movement of the actuator assembly and spindle.
In yet another embodiment, a servo track writing apparatus for securing a head disc assembly (HDA) during a servo track writing process is provided. The apparatus includes a base, a fixed block assembly attached to the base, and a basket assembly opposing the fixed block assembly. The basket assembly includes a movable carriage adapted to receive the HDA. The basket assembly further includes a displacing device adapted for moving the carriage toward the fixed block assembly and a loading device adapted for loading the carriage against the fixed block assembly.
In still yet another embodiment, an apparatus for restraining a head disk assembly (HDA) during a servo track writing operation is provided. Here, the HDA includes a spindle shaft supporting a rotating spindle which in turn supports one or more storage discs. The HDA also has a pivot shaft supporting an actuator assembly for reading and writing from and to the storage discs. The apparatus comprises a device for holding the HDA and a device for restraining each end of the spindle shaft and pivot shaft such that the spindle and actuator assembly are restrained from generally all but rotational motion.
Advantageously, the method and apparatus of the present invention produces disc drives with higher storage capacity than those drives produced by other methods/apparatuses. In particular, the instant invention permits precise, concentric writing of embedded servo information to the disc. By providing external constraint to all but rotational/pivotal motion of the spindle and actuator, the non-repeatable oscillations which frequently occur during servo track writing are minimized. A drive produced according to the present invention thus requires less misregistration budget that is normally required with drives having more eccentric track formation. Thus, the STW of the present invention is capable of producing disc drives with greater track densitiesxe2x80x94and thus higher capacitiesxe2x80x94while utilizing otherwise conventional track writing processes.